There’s a plethora of yield robbers hiding in the soil waiting for the right conditions to attack your crops. With high production costs, it’s critical to protect the seed. Soybean seed prices have risen over 50% since 2003, says Alison Robertson, Iowa State University Extension plant pathologist.
“You want every seed to germinate and become a productive plant,” she says.
Plant stand can be impacted by a number of issues, but some of the most common pests aren’t taken seriously throughout the countryside.
Soybean cyst nematodes (SCN) are a widespread issue, but there’s a lack of awareness and concern for the microscopic roundworm that is the industry’s biggest yield robber, says Greg Tylka, Iowa State University plant pathologist.
“SCN can outlast any soybean farmer,” says Tylka.
SCN-infested fields can have 50% or more yield loss, he explains. It can cause 30% yield loss without showing any visual symptoms.
This common soybean nemesis lives approximately 24 days per generation and produces three to six generations per season. Each female produces more than 200 eggs and is mated by more than one male, explains Tylka. To top it off, the eggs can remain dormant for more than 10 years in the soil.
Different tools are available to manage the pest. Following are three strategies that Tylka recommends.
- Mix up your rotation. “We have to keep growing soybeans, but in the years that you don’t grow soybeans, SCN numbers will drop,” says Tylka.
Nonhost crops like corn can lower SCN populations. Population densities drop annually when nonhost crops are planted and should be considered a management tool. Still, corn-after-corn can’t eliminate populations, says Tylka.
SCN eggs will hatch in three different groups. Most eggs will hatch the next year regardless of a host crop growing. The next group will hatch when a host is grown, but the last group is dormant and won’t hatch for years, says Tylka.
- Plant resistant varieties. Not all SCN-resistant soybean varieties are the same. Each source of resistance possesses four or more genes for SCN resistance, but each source allows for a low level of SCN reproduction. The scientific definition of SCN resistance is supporting no more than 10% reproduction, says Tylka.
SCN populations are becoming resistant to the main resistance gene, PI 88788.
“We’re seeing yields decrease. It’s biological and economical forces at play,” says Tylka. Despite the increasing resistance, resistant varieties with PI 88788 are still yielding relatively well.
Until additional sources of resistance are developed, the resistance will continue to decrease, says Tylka.
- Treat seed if your field has a history of SCN.
“Seed treatments for SCN are a wonderful addition to the toolbox,” says Tylka. However, they aren’t intended to replace resistant varieties. Instead, use seed treatments in combination with other management strategies.
Monitor your cornfields during the growing season and watch the weather to see which diseases will be favorable. Cultural practices can help to manage diseases like northern corn leaf blight (NCLB), says Robertson.
Spores can survive in residue or on host weeds, says Robertson. In addition to selecting seed that scores highly for NCLB resistance, cultural practices such as rotation, residue management, and weed management can help you stay ahead of this disease, says Robertson.
The Disease Triangle
“A lot of our research is focused on understanding the disease triangle,” says Iowa State University Extension plant pathologist Alison Robertson.
“There are three factors that need to be present for a disease to occur,” she says. “There has to be a host, favorable environment, and pathogen.”
Picture one on each side of a triangle. While many pathogens can be present in a field, they won’t cause a disease unless there is both a host and the ideal environment for that specific disease.
Knowing which conditions that different seedling diseases favor allows you to manipulate the conditions at planting to prevent certain seedling diseases.
Pathogens that decrease soybean stands include Pythium, Phytopthora, Rhizoctonia, and Fusarium, says Robertson. Seed treatments are necessary to protect stands when the soils are cold and wet soon after planting, says Robertson.
In 2017, seed treatments would benefit farmers who plant early or when a cold front is imminent, Robertson notes.
Another consideration should be field history, says Robertson. If you know certain fields are riddled with diseases, seed treatments might be worth the extra investment.